The present invention relates to an ATM communication apparatus and a bandwidth control method thereof. More particularly, the present invention relates to an ATM communication apparatus and a bandwidths control method thereof that, in a point/multi-point transmission system, can communicate effectively by dynamically altering bandwidth assignment among optical network units according to upstream traffic situation in an optical line interface in the case where burst signals sent by subscriber terminals connected to the optical network units respectively have originated in a Time Division Multiple Access (TDMA) control technique in which a plurality of the optical network units sends ATM cells according to permission to transmit an upstream cell issued by the optical line interface, the ATM communication apparatus and the bandwidth control method thereof are preferable for application to the point/multi-point transmission system in which the optical line interface provides the subscriber terminals with a plurality of quality of service such as a constant bit rate service, a best effort service or the like. Note that the present invention is not limited to the TDMA technique but can be also applied to the other appropriate multiplex techniques.
As a prior art of the TDMA control method that performs bandwidth assignment, for example, a technology is known that is described in Japanese Patent Laid-Open No. Hei 11(1999)-341037 gazette or the like. This technology is the point/multi-point transmission system in which the optical line interface and a plurality of the opposing optical network units are connected via a splitter and each of the optical network units transmits cells respectively with the time division multiple access control of the optical line interface.
This dynamical bandwidth sharing technique is characterized as described below.    (1) In each of the optical network units, the stored cell quantity of the sending cell buffers and the transmission permit signals of each of the optical network units are transmitted respectively.    (2) The optical line interface periodically supervises the stored quantity of the sending cell buffers and the transmission permit signals of each of the optical network units respectively.    (3) The optical line interface distributes unused transmission domains within transmission frames in accordance with the stored quantity of the sending cell buffers based on the stored quantity of the sending cell buffers and the transmission permit signals notified by each of the optical network units respectively in addition to transmission capacity assigned to the optical network units that require more transmission capacity.
In earlier technology, the above-described dynamical bandwidth sharing control technique allows the service classes with a high burst such as a personal computer communication or the like to use transmission capacity effectively.